Motor controller



Dec 24, 1935. Q sTANsBuRY 2,025,315

MOTOR CONTROLLER Original Filed April 6, 1953 2 Sheets-Sheet l Dec. 24, 1935. c. STANSBURY MOTOR CONTROLLER Original Filed April 6, 1933 2 Sheets-Sheet 2 11.65 as .za a1 Patented Dec. 24, 1935 UNITED STATES PATENT OFFICE MOTOR CONTROLLER Carroll Stansbury, Wauwatosa, Wis., assignor to Cutler-Hammer, Inc. poration of Delaware Milwaukee, Wis., a cor- Application April 6, 1933, Serial No. 664,695

Renewed January 17, 1935 2 Claims. (Cl. 171-242) to maintain a constant average speed ratio but the speed ratio must be the same at any instant, that is, if, for any reason, the speed of one section of the machine varies, the speed of other sections must simultaneously and instantaneously vary in the same ratio.

A well known system heretofore proposed for accomplishing such regulation employs a special form of rheostat in circuit with the field of a direct current motor connected to one section of the machine, and constituting a so-called following motor to be so regulated that its speed is kept in a definite relation to the speed of a so-called leading motor driving another section of the machine. The rheostat comprises a rotating resistor element coupled'to one of the motors and a rotating contact or brush element driven by the other motor and engaging said resistor and being capable of varying its ohmic value. So long as the two elements rotate at exactly the same speed, that is, so long as the speed ratio of the two motors remains the same, the brush stands still relative to the resistor and the ohmic value of the latter in series with. the field winding remains constant; but, if one element is driven at a speed difiering from that of the other element due to a change in the speed ratio of the two motors, a relative movement takes place between the two elements which results in an adjustment of the value of resistance in series with the field of the following motor in such a direction as to tend to correct the speed thereof.

The above-described arrangement has a disadvantage which becomes apparent during the starting up of the following motor, while the leading motor is already running at the proper speed. Under this condition, the brush rotates at a very high speed and thus continuously varies the regulating resistance between its minimum and maximum value thereby causing pulsations in the field strength of the following motor, which is being brought up to speed. As it is not permissible to weaken the field of the motor during the accelerating period, it is necessary that the speed regulating device be rendered inoperative during the accelerating period and be connected in circuit only after the follow- 'ing motor has reached approximately the correct speed ratio with respect to the leading motor.

The proposal discussed is not practical because 6 the relatively large motors required by paper machines necessitate employment of large rheostats and hence it has been proposed to make the resistor stationary and to drive the brush through a differential gearing connected between 10 the leading and following motor in such a manner that the brush stands still when the speed ratio of the motor shafts has a desired value. If, however, the speed ratio of the two shafts should depart from the desired value due 15 to a speed change of either motor, the brush is moved to thereby adjust the value of the resistor in series with the field of the following motor so as to reestablish again the desired speed ratio.

In another type of regulator with a differential drive the brush is connected to a travelling nut, the nut being rotated by one of the motor shafts while an engaging screw is rotated in the same direction by the other shaft. As long as 25 the nut and screw rotate at the same speed the nut does not move laterally and therefore the brush stands still and the field resistance remains constant. If, however, there is a speed difference between the nut and the screw the latter is shifted axially in one direction or the other thereby shifting the contact brush and varying the value of the field resistance in the manner aforedescribed. By terminating the threads on the screw at the two extremes of the brush travel so that the screw turns freely without engaging the threads of the nut, it is possible to permit acceleration of the following motor with constant full field strength as, in this case, the nut and the brush are moved to and held at their extreme full field position.

An object of the present invention is to providea regulator for the aforementioned purpose which is free from the complications inherent in a mechanical differential drive for the field rheostat.

Another object is to provide a. regulator whose action is positive and continuous and which regulates' the field strength in an even and continuous manner.

Another object is to provide a regulator which permits starting of the following motor in a simple manner and without any additional apparatus or manipulations.

The accompanying drawings illustrate one embodiment of the invention together with certain modifications thereof, which will now be described, it being understood that the embodiment illustrated is susceptible of other modifications without departing from the spirit and scope of the appended claims.

In the drawings Figure 1 is a diagram of a paper machine drive embodying the invention.

Fig. 2 is a detailed view of that element of the system shown in Fig. 1 which responds to changes in relative speeds of the two shafts whose speed is to be compared.

Fig. 3 is a cross section of Fig. 2 along the line 33.

Fig. 4 is a vector diagram of certain voltages, the relation of which varies with the relative position and speed of the two shafts.

Fig. 5 is a modification of the details illustrated in Fig. 2.

Fig. 6 illustrates still another form of the apparatus illustrated in Fig. 2, and

Fig. 7 is a. cross section of Fig. 6 along the line 1-1.

The system illustrated in Fig. 1 comprises an electric motor or other prime mover I, to which is coupled the armature of a main direct current generator 2. an auxiliary direct current generator 3 and an alternating current control generator 4.

A paper machine having independent sections 5 and 6 is arranged to have section 5 driven by a leading" motor 1 having an armature 8 and a field winding 9. The armature 8 is connected across the generator 2, whilev the field winding 9 is connected in series with a field regulating rheostat I across the generator 3. It will be understood, however, that leading section of the paper machine may be driven by any other type of prime mover supplied with power and having its speed regulated in any desired way. It is also possible to have the leading motor operate independently of a paper machine section, i. e.

. to have it function solely as a'speed standard of ing I3 is controlled by controlling the voltage 'drop through the resistance M in a manner to be winding I'I forms a connection between the anodes I5 and I6 The center point of the secondary winding I l is connected to a common terminal of the field winding l3 and the resistance I4. The field controller for the motor II further includes a transformer |8 having a primary winding l8 which is connected to the generator 4, and a secondary winding I8 The latter is divided in two equal parts. One end of a non- .shaft 24 so as to. rotate with the latter.

inductive resistance I9 and the grid i5 are connected to the center tap of the winding I8. A second non-inductive resistance 20 is connected in series with the resistance I9. The common terminal of the resistances I9 and 20 is connected to the cathodes I5 and I69, said cathodes being also connected to the positive terminal of generator 3. A non-inductive resistance 2| has one of its terminals connected in series with resistance 20 while the other terminal is connected to one outer terminal of the winding I8. The junction point of resistances and 2| is connected to the grid IIi and also to the other outer terminal of the winding I8 through the coil 23 of a rotatable inductance device 22. l5

One part of the rotatable inductance device 22 carrying the winding 23 is connected through a shaft 24 and variable speed pulleys 25 to the shaft of the motor IL. The other part 3| of the inductance device 22 is driven by any well known 20 rotating synchronous electrical transmission receiver 26 which is supplied with power from a similar device '21 operating as a sender, driven by the leading motor in such a manner that the receiver 26 rotates always in exact syn- 25 chronism with the sender" 21.

The rotatable inductance device 22 is illustrated more in detail in Fig. 2. It consists of a U- shaped laminated frame 28 which carries the inductance coil 23 and which is mounted on the The terminals of the coil 23 are connected to slip rings 29 and 30 respectively, which are mounted on the shaft 24 and which engage corresponding stationary brushes through which the inductance coil 23 is connected in circuit as aforedescribed. An armature 3| is mounted adjacent to the U- shaped frame 28 on a shaft 32 which is in line with shaft 24, said armature being thus rotatable relative to the frame 28. The latter is provided with anon-magnetic stop 33 which limits the counter-clockwise movement of the armature 3| relative to the frame 28 while a stop 34 attached to the armature 3| engages the stop 33 when the armature moves in a clockwise direction relative to the frame 28 through an angle of 90 from the position shown in Figs. 2 and 3. If the armature and the frame are in the relative positions shown in Figs. 2 and 3, the reluctance of the magnetic circuit for coil 23 is a minimum and therefore the inductance of said coil is a maximum, whereas if the armature 3| is rotated in a clockwise direction through an angle of 90 relative to the frame 28, the inductance of the coil 23 is a minimum. The shaft 32 carrying the armature 3| also carries one element 35 of a slip clutch 36, the other element 31 of which is mounted on the shaft 38. This slip clutch may be of any well known design and is arranged in such a manner that it rotates the shaft 32 without relative slippage when the shaft 38 is rotated by the driving element 26 but slips when the armature 3| engages either stop 33 or stop 34.

The operation of the circuit including the inductance coil 23, transformer winding I8 and.

resistances I9, 20 and 2| will now be described with reference to Figs. 1 and 4. The transformers I1 and I8 are connected across a common source of alternating current. Therefore the voltages impressed upon their primary windings I! and IB respectively are in phase, as are also the voltages induced'in the secondary windings I 'I and I8 respectively. The gaseous electron tubes I5 and I6, together with the transformer winding IT", form a full wave rectifier in which, during one half cycle, the potential of the anode l5 is positive with respect to the cathode |5 while that of the anode Iii is negative with respect to that of the cathode l8, and during the succeeding half cycle said polarities are reversed. Therefore, if the tubes l5 and I6 are rendered conducting, a current flows through the resistance l4 to one or the other half of the winding through the tube l5 or IE back to the resistance l4. This current causes a potential difference on the terminals of the resistance l4 and if the circuit'of;

the field winding I3 is connected across the direct current source 3, this potential difference is added to or subtracted from the voltage impressed upon the field by said source and causes a change of the field strength as will be further explained hereinafter,

The voltage induced in the transformer winding I8 is substantially in phase with that induced in the winding l'l The voltage induced in the winding |8 is represented by the vector E in the diagram, Fig. 4. This voltage causes a current flow from the right hand end terminal of the winding I8 through the resistance 2|, the coil 23 of reactance 22, back to the left hand terminal of the winding l8 which current is represented by the vector I, provided that the ohmic values of the resistors l9 and 20 are high relative to the value of the resistor 2|, so that the current fiow from the center tap of the winding Hi over the resistors l9 and 20 may be neglected. The voltage E impressed upon the circuit aforedescribed may be divided into a non-inductive component E which is in phase with the current I and an inductive component E which is 90 out of phase with the former and which is due to the inductive drop in the coil 23. Hence the voltage from the center tap of winding l8 to the common terminal of resistor 2| and reactance 23 is vectorially represented by E that is, the vector from the center of E to the end of the vector E v If the value of the reactance 22 is varied by I relative motion between the frame 28 and the armature 3|, the relation between the voltages E and E varies so that the direction of the vector E relative to the vector E varies, the locus of the vectors E and E being a semi-circle over E as is well known.

Let it be assumed that at the beginning of a given half cycle the potential of the right hand terminal of winding l8 is highly negative with respect to the center tap, and the potential of the center tap is positive with respect to the common terminal of the resistances l9 and 20. If the anode Hi is positive during the same half cycle with respect to the cathode IS, the grid It will be negative with respect to the cathode I6, and no current will flow through the tube I6. If, however, there is a phase displacement between the cathode voltage and the grid voltage, as indicated in Fig. 4, the grid l6 will become positive relative to the cathode H5 at a given moment during the half cycle and the tube IE will conduct current during the rest of such half cycle. During the next half cycle, tube IE will be non-conducting as aforedescribed, but tube |5 will become conducting when the grid |5 becomes positive. The moment when the respective grid becomes positive during the positive half cycle of the corresponding tube' can be varied by varying the value of the inductance 22 as aforedescribed and thus the effective current which passes through the resistance l4 and the voltage drop therethrough can be varied, as will be explained hereinafter.

- the inductance coil 23.

Fig. 5 shows another method of changing the inductance of the coil 23. In this case, the coil 23 is stationary and is equipped with a stationary U- shaped field structure 39 which is adjacent to a shaft 24 and a shaft 40, the latter being driven in turn by the shaft 32 through a coupling M which is in sliding engagement with the shaft 32 and may move longitudinally, being held in angular position relative to shaft 32 by. means of a key 42 and a corresponding key-way. Fastened to the end of shaft 24 is a non-magnetic screw 43 which engages a threaded hole 44 in the end of shaft 40. If there is an angular motion between the shaft 24 and the shaft the latter is moved longitudinally, narrowing or widening the air gap between the adjacent ends of shafts 24 and 40, and as both mentioned shafts are of magnetic material and the frame 39 is mounted adjacent thereto, the reluctance of the magnetic circuit, which is interlinked with the coil 23, varies in accordance with the longitudinal distance between the shafts 24 and 40. Hence relative angular motion between these two shafts produces variations in the inductance of the coil 23 in a manner similar to that aforedescribed in connection with Fig. 2. The advantage of the system shown in Fig. 5 is that both the magnetic frame and the coil are stationary so that no slip rings are required for the connection of the coil.

Instead of employing a variable inductance 23 and a resistance 2| to produce the phase shift of the voltage E in Fig. 3, it is possible to substitute a condenser for the resistor 2| and a resistor for Such a condenser is shown in Fig. 6. Shaft 24 carries an insulating bushing 45 on which is mounted one set of plates 46 of the condenser, these plates being connected with a slip-ring 41. A second set of plates 48 is mounted in the support 49 which is attached to the shaft 32. The second set of condenser plates 48 is connected to the slip ring 5!]. The condenser plates are so shaped as to produce the desired relation between angular displacement and capacity. Suitable stops 5|, 52 limit the maximum relative angular rotation of the plates, as is better illustrated in Fig. 7. The condenser may be connected in circuit by means of the slip ring 41, 59 and engaging brushes. The shaft 32 is connected through a slip clutch 36 to the shaft 38 in the manner aforedescribed in connection with Fig. 2, proportioning of the slip clutch being the same as described already in connection with Fig. 2. The capacity of the condenser remains constant as long as the two shafts 24 and 32 rotate at the same speed and maintain fixed angular position. However, if one of the shafts should rotate faster than the other a change will take place in the capacity of the condenser which will produce a regfiating effect as aforedescribed.

The operation of the system illustrated in Fig. 1 will now be described. The paper machine may be put into operation as follows: The motor I has its armature 8 connected to the generator 2 and its field rheostat i0 is adjusted for the desired speed. The motor then rotates at the desired speed and drives the section 5 and also the synchronous transmitter 21. This causes the synchronous follower 28 to rotate at a corresponding speed thereby rotating the armature 3| of inductance device 22 to the position of maximum inductance. If the field winding l3 of motor H isnow connected-.to the exciter generator 3, a current which is limited by the resistor |4 now flows in this field winding and if the armature I2 is connected to the generator, motor accelerates and drives the section 6 at a low speed. If now the transformers l1 and I8 are also energized, a supplemental voltage is impressed uponrthe resistance l4 which, since the inductance 22 is a maximum, is also maximum and is added to the voltage drop in the resistance l6. This reduces the current in the field winding l3 and causes additional speeding up of motor ll until a speed is reached at which the shaft 24 rotates at the same speed as shaft 32. shaft 24 tends to exceed the speed of shaft 32, a relative motion takcs'place between the magnet frame 28 and the armature 3| thereby varying the impedance of the coil 23 and thus varying in the well known manner the voltage drop through the resistance M and the strength of the current in the winding 13.

If it is desired to vary the speed of the motor ll relative to that of the motor "I, the variable speed device 25 is adjusted.

If it is desired to vary the speed of all the motors simultaneously and at proportional rates, the voltage of the generator 2 may be varied. It is also possible to vary the speed of the motor I by varying its field excitation whereupon the following motors will all automatically have their speed varied through the action of the automatic speed regulating means aforedescribed.

Furthermore, if on slowing down or stopping of the machine as a whole, the leading motor 1 slows down more rapidiy than the following motor II, the reactance device 22 which controls motor II automatically moves to full field position, thus providing dynamic braking action with full field excitation on the following motor. After stopping, the reactance device 22 is left in the position corresponding to the full field excitation of the following motor, and thus puts the latter in condition for the next start. While a slip clutch is shown to limit the relative movement of the reactance members, it is, of course, obvious that any other means may be used to accomplish this result.

Thus it will be apparent that the reactance device 22 not only tends to hold the shafts 24 and 32 in step, but if at any time thecorrective effect As soon as the speed of v is insufficient to keep the two shafts in step, the

' reactance device automatically resumes the position of maximum corrective action in the proper direction. The leading motor I may drive a section of the paper machine or it may be a separate motor; whose sole function is to drive the synchronous transmitter 21 and thus set the pace for the other motors which drive the various sections of the paper machine.

It is to be understood that the invention is not limited to the use of shunt or separately excited motors as illustrated in Figure 1, but that it is equally applicable to any other type of motor and it may be adapted to the control of different motor circuits which are capable of affecting the speed of the motor by having their current controlled in a suitable manner.

It is also to be understood that the invention is not limited to the use of gaseous tubes as described, and it is further possible to omit entirely the electronic tubes and to have the impedance device control directly to the winding of the motor. This is of particular advantage in connection with alternating current, whereby the impedance device may be readily adapted to affect the excitation of the motor.

What I claim as new and desire to secure by Letters Patent is:

1. In a variable reactance device, in combination, with two relatively rotating shafts, of a stationary field member, including a coil, an armature member connected to each shaft, and means to cause lateral movement of said armature members relative to each other in response to relative rotation of said shafts, to thereby vary the reluctance of said reactance device.

2. In a variable reactance device, in combination, with two relatively rotating shafts, of a stationary field member, including a coil, an armature member connected to each shaft, means to cause lateral movement of said armature members relative to each other in response to relative rotation of said shafts to thereby vary the reluctance of said reactance device and a slip clutch to limit said lateral movement.

CARROLL STANSBURY. 

